Kim Kardashian poses during an advertising festival in Cannes, France, in June. The FDA took the socialite to task recently when she promoted a prescription drug on social media without mentioning its risks and usage details. (Lionel Cironneau / Associated Press)

Kim Kardashian's prescription drug flap with the FDA is the latest case of celebrities running into promotional problems on social media.

Buyers -- and followers -- beware.

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Social media, while generally a legitimate celebrity mouthpiece, especially when procured from a verified account, is no longer a place to post thoughts and feelings, but a forum rife with advertising potential and contract obligations that celebrities have to fulfill.

Many stars often don't run their own accounts, are paid to make endorsements to their millions of followers and don't always have that much say over what they can and can't post.

In fact, their social media presence can be bought and sold as part of their promotional agreements for upcoming projects. During last year's Sony hack, it was revealed that ubiquitous actor-comedian Kevin Hart was hired for a few films because of his "social media savvy" and was paid $2 million to tweet about the projects. Incidentally, Hart spoke out about the leak -- and the Sony execs calling him "a whore" -- by defending his empire on social media.

"Glee" alum Lea Michele revealed during her "Scream Queens" Comic-Con panel in July that she would be joining photo-sharing site Snapchat on the day that her Fox horror-comedy "Scream Queens" premieres on Sept. 22. Serendipitous timing, no?

Some may recall another instance of these partnerships going wrong, namely Joan Rivers' posthumous promotion of the iPhone 6 on her Facebook account despite having been dead for several weeks. The deal was suspected to be made before Rivers' untimely death.

Other celebrities have been criticized for the unusual products they promote. The World Wide Web has made once lesser-known overseas endorsements and ad campaigns all the more accessible to celebrities' core audiences at home.

At issue for Kardashian -- she of reality TV fame, the commonplace bathroom selfie and social media prowess -- was that she is a paid spokeswoman for Canadian drug company Duchesnay, which makes the drug she promoted, Diclegis.

The reality star, who has amassed more than 34 million followers, was required to disclose the drug's side effects in the seemingly innocuous tweet and the post has since been taken down at the behest of the U.S. Food and Drug Administration because her remarks omitted its risks and usage details.